1. Field of the Invention
The present invention relates to a shift control apparatus of an automatic transmission and a method therefor, and more particularly to a shift control apparatus of an automatic transmission and a method therefor to reduce shift shock that is generated when a shift lever of an automatic transmission is switched from reverse range xe2x80x98Rxe2x80x99 to forward drive range xe2x80x98Dxe2x80x99 while a vehicle is at standstill.
2. Brief Description of the Prior Art
In general automatic in an transmission of a vehicle, a shift control apparatus determines a target shift level according to all detected conditions such as running speed of a vehicle, openness of a throttle valve, and control oil pressure and controls shifting operations to the target shift stage.
In a prior art automatic transmission, the shifting operations to the target shift level involve fictional elements and changing from a released state to an operational state. Shift shock is generated depending on operational states of those frictional elements.
Accordingly, a variety of techniques have been developed and applied to reduce such shift shock. For instance, in order to reduce the shift shock at the beginning and end of shifting operations when the shift lever is switched from neutral range xe2x80x98Nxe2x80x99 to reverse range xe2x80x98Rxe2x80x99, an accumulator is mounted onto a low/reverse brake, which is an operational element in an oil pressure circuit of an automatic transmission which buffers the oil pressure that is supplied to the low/reverse brake.
However, since the accumulator provides a buffering operation of oil pressure that is supplied to the low/reverse brake, the accumulator has a slow shift response to the release of oil pressure. If the shift lever of an automatic transmission is directly switched from reverse range xe2x80x98Rxe2x80x99 to forward drive range xe2x80x98Dxe2x80x99, the oil pressure of a servo-apply (S/A) is added, before oil pressure of the low/reverse brake is completely released, which results in the shift shock.
The present invention solves the aforementioned problem and provides a shift control apparatus of an automatic transmission and a method therefor to reduce shift shock by detecting a lapsed time of a shift lever set at neutral range xe2x80x98Nxe2x80x99, when the shift lever is switched from reverse range xe2x80x98Rxe2x80x99 to forward drive range xe2x80x98Dxe2x80x99 and the oil temperature of the transmission and controlling the shifting oil pressure according to the detected values.
The present invention is a shift control apparatus of an automatic transmission of a vehicle, the apparatus comprising:
vehicle operation detecting means for checking an operational state of a vehicle;
shift control means for calculating a lapsed time of a shift lever set at neutral range xe2x80x98Nxe2x80x99 when the shift lever is switched from reverse range xe2x80x98Rxe2x80x99 to neutral range xe2x80x98Nxe2x80x99 with an input of a signal detected by the vehicle operation detecting means and for outputting a shift control duty signal to control the shift oil pressure according to the lapsed time and the oil temperature detected by the vehicle operation means when the shift lever is switched from neutral range xe2x80x98Nxe2x80x99 to forward drive range xe2x80x98Dxe2x80x99; and
drive means for performing shifting operations by providing a frictional element with oil pressure duty-controlled by a shift control duty signal output by the shift control means and discharged by an oil pump.
A shift control method of an automatic transmission of a vehicle, in accordance with the invention comprises the steps of:
discriminating whether a shift lever of the automatic transmission is switched from reverse range xe2x80x98Rxe2x80x99 to neutral range xe2x80x98Nxe2x80x99;
calculating a lapsed time when the shift lever is set at neutral range xe2x80x98Nxe2x80x99, if it is confirmed that the shift lever is switched from reverse range xe2x80x98Rxe2x80x99 to neutral range xe2x80x98Nxe2x80x99 at the previous step, and discriminating whether the shift lever is switched from neutral range xe2x80x98Nxe2x80x99 to forward drive range xe2x80x98Dxe2x80x99; and
performing shifting operations with a different shifting oil pressure depending on the lapsed time when the shift lever is set at the neutral range xe2x80x98Nxe2x80x99 if it is confirmed that the shift lever is switched from neutral range xe2x80x98Nxe2x80x99 to the forward drive range xe2x80x98Dxe2x80x99 at the previous step.